1 /*
   2  * Copyright (c) 1999, 2005, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang;
  27 
  28 
  29 /**
  30  * Package-private utility class containing data structures and logic
  31  * governing the virtual-machine shutdown sequence.
  32  *
  33  * @author   Mark Reinhold
  34  * @since    1.3
  35  */
  36 
  37 class Shutdown {
  38 
  39     /* Shutdown state */
  40     private static final int RUNNING = 0;
  41     private static final int HOOKS = 1;
  42     private static final int FINALIZERS = 2;
  43     private static int state = RUNNING;
  44 
  45     /* Should we run all finalizers upon exit? */
  46     private static boolean runFinalizersOnExit = false;
  47 
  48     // The system shutdown hooks are registered with a predefined slot.
  49     // The list of shutdown hooks is as follows:
  50     // (0) Console restore hook
  51     // (1) Application hooks
  52     // (2) DeleteOnExit hook
  53     private static final int MAX_SYSTEM_HOOKS = 10;
  54     private static final Runnable[] hooks = new Runnable[MAX_SYSTEM_HOOKS];
  55 
  56     // the index of the currently running shutdown hook to the hooks array
  57     private static int currentRunningHook = 0;
  58 
  59     /* The preceding static fields are protected by this lock */
  60     private static class Lock { };
  61     private static Object lock = new Lock();
  62 
  63     /* Lock object for the native halt method */
  64     private static Object haltLock = new Lock();
  65 
  66     /* Invoked by Runtime.runFinalizersOnExit */
  67     static void setRunFinalizersOnExit(boolean run) {
  68         synchronized (lock) {
  69             runFinalizersOnExit = run;
  70         }
  71     }
  72 
  73 
  74     /**
  75      * Add a new shutdown hook.  Checks the shutdown state and the hook itself,
  76      * but does not do any security checks.
  77      *
  78      * The registerShutdownInProgress parameter should be false except
  79      * registering the DeleteOnExitHook since the first file may
  80      * be added to the delete on exit list by the application shutdown
  81      * hooks.
  82      *
  83      * @params slot  the slot in the shutdown hook array, whose element
  84      *               will be invoked in order during shutdown
  85      * @params registerShutdownInProgress true to allow the hook
  86      *               to be registered even if the shutdown is in progress.
  87      * @params hook  the hook to be registered
  88      *
  89      * @throw IllegalStateException
  90      *        if registerShutdownInProgress is false and shutdown is in progress; or
  91      *        if registerShutdownInProgress is true and the shutdown process
  92      *           already passes the given slot
  93      */
  94     static void add(int slot, boolean registerShutdownInProgress, Runnable hook) {
  95         synchronized (lock) {
  96             if (hooks[slot] != null)
  97                 throw new InternalError("Shutdown hook at slot " + slot + " already registered");
  98 
  99             if (!registerShutdownInProgress) {
 100                 if (state > RUNNING)
 101                     throw new IllegalStateException("Shutdown in progress");
 102             } else {
 103                 if (state > HOOKS || (state == HOOKS && slot <= currentRunningHook))
 104                     throw new IllegalStateException("Shutdown in progress");
 105             }
 106 
 107             hooks[slot] = hook;
 108         }
 109     }
 110 
 111     /* Run all registered shutdown hooks
 112      */
 113     private static void runHooks() {
 114         for (int i=0; i < MAX_SYSTEM_HOOKS; i++) {
 115             try {
 116                 Runnable hook;
 117                 synchronized (lock) {
 118                     // acquire the lock to make sure the hook registered during
 119                     // shutdown is visible here.
 120                     currentRunningHook = i;
 121                     hook = hooks[i];
 122                 }
 123                 if (hook != null) hook.run();
 124             } catch(Throwable t) {
 125                 if (t instanceof ThreadDeath) {
 126                     ThreadDeath td = (ThreadDeath)t;
 127                     throw td;
 128                 }
 129             }
 130         }
 131     }
 132 



 133     /* The halt method is synchronized on the halt lock
 134      * to avoid corruption of the delete-on-shutdown file list.
 135      * It invokes the true native halt method.
 136      */
 137     static void halt(int status) {
 138         synchronized (haltLock) {
 139             halt0(status);
 140         }
 141     }
 142 
 143     static native void halt0(int status);
 144 
 145     /* Wormhole for invoking java.lang.ref.Finalizer.runAllFinalizers */
 146     private static native void runAllFinalizers();
 147 
 148 
 149     /* The actual shutdown sequence is defined here.
 150      *
 151      * If it weren't for runFinalizersOnExit, this would be simple -- we'd just
 152      * run the hooks and then halt.  Instead we need to keep track of whether
 153      * we're running hooks or finalizers.  In the latter case a finalizer could
 154      * invoke exit(1) to cause immediate termination, while in the former case
 155      * any further invocations of exit(n), for any n, simply stall.  Note that
 156      * if on-exit finalizers are enabled they're run iff the shutdown is
 157      * initiated by an exit(0); they're never run on exit(n) for n != 0 or in
 158      * response to SIGINT, SIGTERM, etc.
 159      */
 160     private static void sequence() {
 161         synchronized (lock) {
 162             /* Guard against the possibility of a daemon thread invoking exit
 163              * after DestroyJavaVM initiates the shutdown sequence
 164              */
 165             if (state != HOOKS) return;
 166         }
 167         runHooks();
 168         boolean rfoe;
 169         synchronized (lock) {
 170             state = FINALIZERS;
 171             rfoe = runFinalizersOnExit;
 172         }
 173         if (rfoe) runAllFinalizers();
 174     }
 175 
 176 
 177     /* Invoked by Runtime.exit, which does all the security checks.
 178      * Also invoked by handlers for system-provided termination events,
 179      * which should pass a nonzero status code.
 180      */
 181     static void exit(int status) {
 182         boolean runMoreFinalizers = false;
 183         synchronized (lock) {
 184             if (status != 0) runFinalizersOnExit = false;
 185             switch (state) {
 186             case RUNNING:       /* Initiate shutdown */
 187                 state = HOOKS;
 188                 break;
 189             case HOOKS:         /* Stall and halt */
 190                 break;
 191             case FINALIZERS:
 192                 if (status != 0) {
 193                     /* Halt immediately on nonzero status */
 194                     halt(status);
 195                 } else {
 196                     /* Compatibility with old behavior:
 197                      * Run more finalizers and then halt
 198                      */
 199                     runMoreFinalizers = runFinalizersOnExit;
 200                 }
 201                 break;
 202             }
 203         }
 204         if (runMoreFinalizers) {
 205             runAllFinalizers();
 206             halt(status);
 207         }
 208         synchronized (Shutdown.class) {
 209             /* Synchronize on the class object, causing any other thread
 210              * that attempts to initiate shutdown to stall indefinitely
 211              */

 212             sequence();
 213             halt(status);
 214         }
 215     }
 216 
 217 
 218     /* Invoked by the JNI DestroyJavaVM procedure when the last non-daemon
 219      * thread has finished.  Unlike the exit method, this method does not
 220      * actually halt the VM.
 221      */
 222     static void shutdown() {
 223         synchronized (lock) {
 224             switch (state) {
 225             case RUNNING:       /* Initiate shutdown */
 226                 state = HOOKS;
 227                 break;
 228             case HOOKS:         /* Stall and then return */
 229             case FINALIZERS:
 230                 break;
 231             }
 232         }
 233         synchronized (Shutdown.class) {
 234             sequence();
 235         }
 236     }
 237 
 238 }
--- EOF ---